Light-induced olefin metathesis
23 Nov 2010-Beilstein Journal of Organic Chemistry (Beilstein-Institut)-Vol. 6, Iss: 1, pp 1106-1119
TL;DR: This survey of the relevant literature summarises past and present developments in the use of light to expedite olefin ring-closing, ring-opening polymerisation and cross-metathesis reactions.
Abstract: Light activation is a most desirable property for catalysis control. Among the many catalytic processes that may be activated by light, olefin metathesis stands out as both academically motivating and practically useful. Starting from early tungsten heterogeneous photoinitiated metathesis, up to modern ruthenium methods based on complex photoisomerisation or indirect photoactivation, this survey of the relevant literature summarises past and present developments in the use of light to expedite olefin ring-closing, ring-opening polymerisation and cross-metathesis reactions.
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TL;DR: This paper presents a new mesoporous composite material developed at the University of Texas at Austin that combines high-performance liquid chromatography with low-tech engineering techniques to fabricate high-tech composite materials.
Abstract: Aaron J. Teator,†,‡,∥ Dominika N. Lastovickova,†,‡,∥ and Christopher W. Bielawski*,‡,§ †Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States ‡Center for Multidimensional Carbon Materials (CMCM), Institute for Basic Science (IBS) and Departments of Chemistry and Energy Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, Republic of Korea
247 citations
207 citations
TL;DR: A short review of the role of photocatalysts in photopolymerization reactions is presented in this article, where a special emphasis is placed on photoredox catalysts leading to high-performance initiating systems for polymerization upon low light intensity for the use of light emitting diodes (LEDs) and/or visible light.
Abstract: A short review of the role of photocatalysts in photopolymerization reactions is presented. A special emphasis is placed on photoredox catalysts leading to i) high-performance initiating systems for polymerization upon low light intensity for the use of light emitting diodes (LEDs) and/or visible light and ii) controlled radical photopolymerization (CRP2) processes with formation/reactivation of dormant species triggered by light.
124 citations
TL;DR: Metal carbonyl-mediated reactions are reported that are of considerable interest for the synthesis of complex polyfunctionalized compounds and develop synergistic effects in the sense of "Green Chemistry".
Abstract: Since the time of Giacomo Ciamician at the beginning of the 20th century, photochemical transformations have been recognized as contributing to sustainable chemistry. Electronic excitation significantly changes the reactivity of chemical compounds. Thus, the application of activation reagents is frequently avoided and transformations can be performed under mild conditions. Catalysis plays a central role in sustainable chemistry. Stoichiometric amounts of activation reagents are often avoided. This fact and the milder catalytic reaction conditions diminish the formation of byproducts. In the case of homogeneous catalysis, organometallic compounds are often applied. The combination of both techniques develops synergistic effects in the sense of “Green Chemistry”. Herein, metal carbonyl-mediated reactions are reported. These transformations are of considerable interest for the synthesis of complex polyfunctionalized compounds. Copper(I)-catalyzed [2+2] photocycloaddition gives access to a large variety of cyclobutane derivatives. Currently, a large number of publications deal with photochemical electron-transfer-induced reactions with organometallic and coordination compounds, particularly with ruthenium complexes. Several photochemically induced oxidations can easily be performed with air or molecular oxygen when they are catalyzed with organometallic complexes. Photochemical reaction conditions also play a certain role in CH activation with organometallic catalysts, for instance, with alkanes, although such transformations are conveniently performed with a variety of other photochemical reactions.
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References
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TL;DR: The discussion includes an analysis of trends in catalyst activity, a description of catalysts coordinated with N-heterocyclic carbene ligands, and an overview of ongoing work to improve the activity, stability, and selectivity of this family of L2X2Ru=CHR complexes.
Abstract: In recent years, the olefin metathesis reaction has attracted widespread attention as a versatile carbon−carbon bond-forming method. Many new applications have become possible because of major advances in catalyst design. State-of-the-art ruthenium catalysts are not only highly active but also compatible with most functional groups and easy to use. This Account traces the ideas and discoveries that were instrumental in the development of these catalysts, with particular emphasis on (PCy3)2Cl2RuCHPh and its derivatives. The discussion includes an analysis of trends in catalyst activity, a description of catalysts coordinated with N-heterocyclic carbene ligands, and an overview of ongoing work to improve the activity, stability, and selectivity of this family of L2X2RuCHR complexes.
3,229 citations
TL;DR: These air- and water-tolerant complexes were shown to exhibit an increased ring-closing metathesis activity at elevated temperature when compared to that of the parent complex 2 and the previously developed complex 3.
3,127 citations
TL;DR: In this paper, the authors provide an overview of the development of catalysts for olefin metathesis which combine high activity, durability, and excellent tolerance towards polar functional groups.
Abstract: The advent of well-defined catalysts for olefin metathesis which combine high activity, durability, and excellent tolerance towards polar functional groups has revolutionized the field. The past decade has seen the rapid embrace of these reagents as tools for advanced organic and polymer chemistry and the success of this development is witnessed by a plethora of elegant applications to the synthesis of natural and nonnatural products. This review article provides an overview of these developments and intends to familiarize the reader with some very recent advances which hold the promise to expand the scope of the reaction even further. Moreover, the positive impact of metathesis on the fundamental logic of retrosynthetic planning is demonstrated by means of typical examples. Finally, it will be shown that metathesis is by no means restricted to alkenes as substrates, and some comments on metathesis reactions following unconventional mechanistic pathways will also be presented.
1,614 citations
TL;DR: A self-healing system capable of autonomously repairing repeated damage events via a three-dimensional microvascular network embedded in the substrate is reported, opening new avenues for continuous delivery of healing agents for self-repair as well as other active species for additional functionality.
Abstract: Self-healing polymers composed of microencapsulated healing agents exhibit remarkable mechanical performance and regenerative ability, but are limited to autonomic repair of a single damage event in a given location. Self-healing is triggered by crack-induced rupture of the embedded capsules; thus, once a localized region is depleted of healing agent, further repair is precluded. Re-mendable polymers can achieve multiple healing cycles, but require external intervention in the form of heat treatment and applied pressure. Here, we report a self-healing system capable of autonomously repairing repeated damage events. Our bio-inspired coating-substrate design delivers healing agent to cracks in a polymer coating via a three-dimensional microvascular network embedded in the substrate. Crack damage in the epoxy coating is healed repeatedly. This approach opens new avenues for continuous delivery of healing agents for self-repair as well as other active species for additional functionality.
1,415 citations
TL;DR: A review of living ring-opening metathesis polymerization (ROMP) reactions can be found in this article, along with a discussion of state-of-the-art catalysts for use in living ROMP reactions as well as opportunities for the future.
1,244 citations